Proficiency test of pH,conductivity and dissolved oxygen concentration field measurements in river water

In 2013, Proftest SYKE organised the first proficiency test (PT) in Finland for field measurements of temperature, conductivity, dissolved oxygen concentration, oxygen saturation and pH value in river water. The aim was to pilot the organisation of an in situ proficiency test—particularly, how to select the test location—and how to assess the homogeneity and stability of the measurement site and the water to be tested. The focus was also to evaluate the suitability of the common field sensors used for water analysis, as well as the comparability of the results between the instruments under field conditions. The overall application of quality assurance procedures was also surveyed. This paper deals with the results, findings and recommendations for the measurement of pH, conductivity and dissolved oxygen concentration. In total, nine participants with 16 sensors took part in the proficiency test. For the evaluation of the performance of each participant, z scores were calculated allowing 3 % to 8 % deviation from the assigned value. The standard deviation of the participant’s results was lower than organiser expected, and 80 % of the results for pH, 79 % for conductivity and 69 % for dissolved oxygen concentration were regarded as satisfactory. According to the results, the most challenging measurement was for dissolved oxygen with a Clark cell-type measurement principle based on electrochemical reaction. All sensors tested in the PT were less than 5 years, old and they were calibrated according to the manufacturer’s instructions. None of the participants had estimated measurement uncertainty for their sensor measurements. In addition, internal and external quality assurance protocols were usually lacking.     

Characterisation of poly(ethylene oxide) sulfonic acids

PEO sulfonic acids with M_w in the range 446–4246 have been prepared. Mechanically stable polyelectrolyte films containing high molar mass PEO and PEO sulfonic acids were prepared. The PEO sulfonic acids and the polyelectrolyte films were examined by thermal analysis, optical microscopy, Raman spectroscopy, and impedance spectroscopy. While the low molar mass PEO sulfonic acids were completely amorphous, sulfonic acids with M_w ≥ 1246 show considerable crystallinity. Experimental data indicate aggregation of the low molar mass PEO sulfonic acids through hydrogen bonds. The PEO sulfonic acids are miscible with high molar mass PEO and form free standing polyelectrolyte films. The PEO sulfonic acids with the lowest molar masses have a plasticizing effect on the high molar mass PEO. The crystallinity of the films decreased as the concentration of sulfonic acid increased. The films are stable at RH ≤ 75%, and for some mixtures protonic conductivities of 10⁻³ S cm⁻¹ at room temperature were reached.     

Measurement of elastic light scattering from two optically trapped microspheres and red blood cells in a transparent medium

Optical tweezers can be used to manipulate small objects and cells. A trap can be used to fix the position of a particle during light scattering measurements. The places of two separately trapped particles can also be changed. In this Letter we present elastic light scattering measurements as a function of scattering angle when two trapped spheres are illuminated with a He-Ne laser. This setup is suitable for trapping noncharged homogeneous spheres. We also demonstrate measurement of light scattering patterns from two separately trapped red blood cells. Two different illumination schemes are used for both samples.     

On Beckenbach–Radó type integral inequalities

Beckenbach and Radó characterized logarithmically subharmonic functions in the plane in terms of integral inequalities involving spherical averages. In this work we generalize this result to higher dimensions and thus answer to a question raised by Beckenbach and Radó. We also consider generalizations of integral inequalities suggested by Beckenbach and Radó and discuss connections to reverse Hölder inequalities and Muckenhoupt weights.     

Regularity of Sets with Quasiminimal Boundary Surfaces in Metric Spaces

This paper studies regularity of perimeter quasiminimizing sets in metric measure spaces with a doubling measure and a Poincaré inequality. The main result shows that the measure-theoretic boundary of a quasiminimizing set coincides with the topological boundary. We also show that such a set has finite Minkowski content and apply the regularity theory to study rectifiability issues related to quasiminimal sets in the strong A _∞-weighted Euclidean case.     

Tracing Lysozyme-Lipid Interactions with Long-Wavelength Squaraine Dyes

The applicability of the two newly commercial available squaraine labels Square-670-NHS and Seta-635-NHS to exploring protein-lipid interactions has been evaluated. The labels were conjugated to lysozyme (Lz) (squaraine-lysozyme conjugates below referred to as Square-670-Lz and Seta-635-Lz), a structurally well-characterized small globular protein displaying the ability to interact both, electrostatically and hydrophobically with lipids. The lipid component of the model systems was represented by lipid vesicles composed of zwitterionic lipids egg yolk phosphatidylcholine (PC) and 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and their mixtures with anionic lipids either beef heart cardiolipin (CL) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), respectively. Fluorescence intensity of Square-670-Lz was found to decrease upon association with lipid bilayer, while the fluorescence intensity of Seta-635-Lz displayed more complex behavior depending on lipid-to-protein molar ratio. Covalent coupling of squaraine labels to lysozyme exerts different influence on the properties of dye-protein conjugate. It was suggested that Square-670-NHS covalent attachment to Lz molecule enhances protein propensity for self-association, while squaraine label Seta-635-NHS is sensitive to different modes of lysozyme-lipid interactions—within the L:P range 6–11, when hydrophobic protein-lipid interactions are predominant, an aggregation of membrane-bound protein molecules takes place, thereby decreasing the fluorescence intensity of Seta-635-Lz. At higher L:P values (from 22 to 148) when electrostatic interactions are enhanced fluorescence intensity of Seta-635-Lz increases with increasing lipid concentrations.     

Thermal phase behavior of DMPG: the exclusion of continuous network and dense aggregates

1,2-Dimyristoyl-sn-glycero-3-phospho-rac-glycerol has been suggested to form at intermediate temperatures and at high concentrations in low-salt solutions as a continuous sponge phase (Heimburg, T.; Biltonen, R. L. Biochemistry 1994, 33, 9477-9488). In the present study, the changes in signals seen for a range of fluorescent probes during phase transformations of this phospholipid indicate continuous melting and a change in lipid packing, in accordance with previous reports. However, in accordance with Lamy-Freund and Riske (Lamy-Freund, M. T.; Riske, K. A. Chem. Phys. Lipids 2003, 122, 19-32), no enhancement of lipid mixing within the putative sponge phase region was seen, suggesting a lack of a connected lipid surface. Accordingly, a typical sponge phase cannot account for the properties of the intermediate phase. The low scattering intensities of the latter have also been taken as evidence for disaggregation. While dynamic light scattering and data for membranes containing poly(ethylene glycol)-ylated lipids could lend credence to disaggregation, the most likely explanation for the scattering data would appear to be a shape transition without significant changes in neither vesicle aggregation nor bilayer connectivity. An abrupt change in light scattering and signals from some of the fluorescent probes used reveals a new transition at Tt approximately 43 degrees C, with the formation of a more ordered interface.     

Self-organized nanostructures of poly(4-vinylpyridine), polyaniline and polyamides due to metal complexation

Comb-shaped supramolecules are constructed using flexible polymers and semi-rigid conjugated undoped or doped conjugated polymers upon complexing Zinc dodecyl benzene sulphonate, Zn(DBS)₂. Selforganized nanostructures are formed in the bulk due to competing attractive interactions (coordination or water mediated hydrogen bonding) and repulsive polar/nonpolar interactions, showing characteristic long periods of ca. 30 Å.     

Morphology of dry lignins and size and shape of dissolved kraft lignin particles by X-ray scattering

Lignin is a highly branched polymer consisting of phenylpropane units, and it is one of the ingredients of the supporting matrix in plant cell walls. The morphology of several lignins extracted from plant cell walls using different methods was studied by small-angle and ultra-small-angle X-ray scattering. A power-law type intensity was observed for the dry lignins, but on the basis of the power-law exponent the fractal approach often applied to lignins is not fully justified. However, the intensity of kraft lignin did show a power law with surface fractal dimension D(s) = 2.7 +/- 0.1. The specific surface area of the lignins ranged from about 0.5 to 60 m(2)/g with 20% relative accuracy. The radius of gyration was determined from small-angle X-ray scattering data for aqueous solutions of kraft lignin. The shape of the particles in NaCl and NaOH solutions was found to be elongated. The particles were about 1-3 nm thick, while the length (5-9 nm) depended on the solvent and on the lignin concentration. The size of these primary particles was approximately the same as the size of the pores in the fractal aggregates of the dry kraft lignin. Their size was determined to be about 3.5 nm.